1 of my cordless phones keeps saying Connecting...

Does it work when moved closer to the base unit? What the make and model of the phone system?

No it doesn't work-I'm right next to base unit. 

AT&T DECT 6.0

Model: CL82409

Thanks for your help.

Has it ever worked? Is this a new handset you're trying to add or replace another one with?

It is not a new handset. However, I moved it from 1 room to another (after Father died) - am unsure if he previously had a problem.  Thank you for your help.  It looks like I need to replace this 1 phone.